Refining of iron

ABSTRACT

THE INVENTION IS CONCERNED WITH THE REFINING OR TREATMENT OF MOLTEN METALS AND HAS PARTICULAR REFERENCE TO THE REFINING OF STEEL. A PROCESS FOR THE REFINING OR TREATMENT OF THE MELT INCLUDES THE STEP OF SUBJECTING THE MELT TO AN OXYGEN TREATMENT WITHIN A REFINING VESSEL BY INJECTING INTO THE VESSEL A STREAM OF NASCENT OXYGEN, NASCENT HYDROGEN AND HYDROXYL RADICALS AND CAUSING OR ALLOWING SAID RADICALS TO ENTER THE MELT AND RECOMBINE EXOTHERMALLY IN THE MELT OR ON THE SURFACE OF THE MELT. THE NASCENT OXYGEN, NASCENT HYDROGEN AND HYDROXYL FREE RADICALS MAY BE GENERATED BY MEANS OF A PLASMA ARE OR BY MEANS OF A FLAME FED BY STREAMS OF OXYGEN AND GASEOUS CARBONACEOUS FUEL UNTIL REFINING IS COMPLETE, ADJUSTING THE PROPORTIONS OF OXYGEN TO FUEL TO OBTAIN SUBSTANTIALLY COMPLETE COMBUSTION AND LOCATING THE FLAME WITHIN THE VESSEL SO THAT THE PRODUCTS OF COMBUSTION BUT NOT THE FLAME ITSELF IMPINGES UPON THE MELT.

Patented June 8, 1971 U.S. CI. 75-60 5 Claims ABSTRACT OF THE DISCLOSURE The invention is concerned with the refining or treatment of molten metals and has particular reference to the refining of steel. A process for the refining or treatment of the melt includes the step of subjecting the melt to an oxygen treatment within a refining vessel by injecting into the vessel a stream of nascent oxygen, nascent hydrogen and hydroxyl radicals and causing or allowing said radicals to enter the melt and recombine exothermally in the melt or on the surface of the melt. The nascent oxygen, nascent hydrogen and hydroxyl free radicals may be generated by means of a plasma are or by means of a flame fed by streams of oxygen and gaseous carbonaceous fuel until refining is complete, adjusting the proportions of oxygen to fuel to obtain substantially complete combustion and locating the flame within the vessel so that the products of combustion but not the flame itself impinges upon the melt.

Applicant claims priority under 35 U.S.C. 1-19 for application Ser. No. 5'5,839/ 67 filed in the British Patent Otfice on Dec. '8, 1967.

The present invention relates to the refining or treatment of molten metals and has particular reference to an improved process for the refining of steel in an L.D. or B.O.F. converter or in an open hearth furnace.

According to the present invention, there is provided a process for the refining or treatment of metals which process includes the step of subjecting a melt of the metal to an oxygen treatment within a refining vessel until the refining or treatment is complete, by injecting into the vessel a stream of nascent oxygen, nascent hydrogen and hydroxyl radicals and causing or allowing said radicals to enter the melt and recombine exothermally in the melt and/or on the surface of the melt.

The present invention also includes a process for production of steel in an open hearth furnace or in a top blown converter which process comprises injecting into the refining vessel a stream of nascent oxygen, nascent hydrogen and hydroxyl radicals and causing or allowing said radicals to enter the melt and recombine exothermally in the melt and/or on the surface of the melt.

The stream of nascent oxygen, nascent hydrogen and hydroxyl free radicals may be generated by means of a plasma are or by means of a flame fed by streams of oxygen and gaseous carbonaceous fuel until the refining is completed, adjusting the proportions of oxygen to fuel to obtain substantially complete combustion and locating the flame within the vessel so that the products of combustion but not the flame itself impinge upon the melt.

It is preferred that there is an excess of oxygen over the quantity required to effect complete combustion of the fuel the excess may be greater than 1000% of that required to obtain complete combustion of the fuel. Alternatively, the excess of oxygen may typically be within the range to 200%.

The gaseous carbonaceous fuel may be a natural gas consisting substantially of methane and ethane or any other suitable gaseous hydrocarbon fuel such, for example, as waste or exhaust gases from a petroleum refining plant.

The streams of oxygen and gaseous fuel may be injected into the refining vessel by means of a multi-jet blowing nozzle such as that forming the subject of British complete specification No. 1,021,099 corresponding to U.S. Pat. 3,313,535. During refining, the flame should not impinge upon the melt in order to reduce contamination of the melt by introduction of sulphur thereinto.

The oxygen may be preheated in the nozzle or in the flame since it will be appreciated that in the process using a conventional top blown converter as hitherto employed the oxygen used is cold and in fact will be further cooled by adiabatic expansion which takes place when the oxygen is emitted from the nozzle and this constitutes a considerable drain on the heat produced in the reactions of the process and thus limits the quantity of any scrap which may be charged to the melt prior to or during the refining process.

In a conventional top blown converter, the oxygen required for refining a ferrous charge to steel is for example, 2,000 cubic foot per ton of steel produced. The process of the present invention results in the production of an extremely hot flame which enables the temperature of the charge in the converter to be controlled during the reaction by, if necessary, varying the proportion of gaseous fuel to oxygen in the mixture. The present invention permits a considerably larger proportion of scrap to be used as calculated from the heat of com bustion of the quantity of the gaseous fuel and the heat required to raise the scrap to tapping temperature. How ever, the scrapaddition must be calculated having regard to the need to maintain a careful heat balance during the process. v

It has been found that by using the process of the present invention, a considerable reduction in the production of fume results during steel making and consequently such use may reduce the level of fume to that acceptable by the Health Authorities.

The gaseous fuel oxygen mixture may be injected into the refining vessel by means of a multi-jet blowing nozzle which may be incorporated at the end of a blowing lance such as that described and claimed in our British complete specification Ser. No. 1,021,099 corresponding to U.S. Pat. 3,313,535 which comprises an elongate body member having a fuel supply conduit centrally located therein, and an oxygen supply conduit surrounding said fuel supply conduit to provide an annular passageway for the supply of oxygen, wherein the body member is provided with a delivery nozzle at one end thereof formed with a plurality of discharge orifices and communicating with said oxygen supply conduit through a plurality of oxygen supply pipes disposed at an angle through the longitudinal axis of the lance and wherein the fuel supply conduit is provided at its outlet end with a plurality of fuel supply pipes extending therefrom and each having its end portion situated in a corresponding oxygen supply pipe so that oxygen flowing through said supply pipes to the discharge orifices will flow in an annulus around the end of the corresponding fuel supply pipes whereby fuel will be entrained in the oxygen supplies when discharged from the discharge orifices.

Some modification of the lance is, however, necessary in order to adapt such a lance for use with an L.D. or B.O.F. steel making apparatus. The length of the lance is substantially increased and consequently there is a possibility of excessive cooling of the gaseous fuel due to its travel down the lance. This cooling may be prevented by lagging the gaseous fuel supply pipe or by providing an additional pipe outside the gaseous fuel supply pipe leaving a gap so as to provide a resistance to heat transfer.

In use, with an open top blown converter, the lance is located towards the top of the converter and the oxygen and gaseous fuel supplied to the lance is turned on. The mixture is ignited at the nozzle outlet to provide a flame extending some 1.5 ft. to 2 ft. from the end of the discharge orifices in the lance. The lance is then lowered so that the discharge orifices are within 4 to 6 ft. from the surface of the melt, that is to say, so that the flame per se does not impinge upon the melt surface. The supply of the oxygen and gaseous fuel mixture is continued until the refining operation is complete. It is noted that there is a considerable reduction of fume produced during the operation and it is possible to make visual observation of the material within the refining vessel.

In a typical example of the process of the present invention a refining vessel was charged as follows:

Lbs. Hot metal 274,000 Scrap 185,000 Lime 29,000

The hot metal was molten pig iron at a temperature of 1400" C. and the hot metal analysis was as follows:

Percent by weight Carbon 4.45 Silicon 1.18 Manganese 0.90 Phosphorus 0.09 Sulphur 0.036

the balance apart from incidental impurities being of iron.

A blowing lance having a construction specifically disclosed in British complete specification No. 1,021,099 corresponding to US. Patent 3,313,535 was located with the discharge nozzles just within the top of the vessel and spaced some 16- ft. from the surface of the melt within the vessel. The fuel supply conduits within the lance were connected to a natural gas supply capable of supplying natural gas having the following analysis:

Percent by weight Methane 82 Ethane 17 Nitrogen 1 CV. Rating approximately 1000 B.t.u. per cubic foot. Oxygen was supplied to the lance to issue from the discharge orifices at a rate of 10,000 cubic foot per minute the period of the reaction, that is to say, for a period of 26 minutes during the course of which the 29,000 lbs. of lime was added to flux the slag. During the course of the reaction it was noted that little fume was produced and it was possible to observe the surface of the melt during the reaction. When the reaction was complete the supply of oxygen and gaseous fuel was terminated and the molten steel was tapped from the vessel.

It was found that the steel produced by this process was a good quality and had a low sulphur content, the principal steel analysis being as follows:

Percent by weight Carbon 0.055 Manganese 0.070 Phosphorus 0.005 Sulphur 0.025 the balance being of iron apart from the incidental impurities.

What is claimed is:

1. A process for refining molten iron by subjecting a melt to refining gases comprising:

(A) creating a flame in a converter vessel and preventing said flame from impinging the melt;

(B) feeding said flame with a stream of oxygen and gaseous fuel, said oxygen being in an amount at least sufficient to obtain complete combustion of the gaseous fuel; and

(C) impinging any uncombined oxygen and products of combustion upon said melt until refining is complete.

2. A process as set forth in claim 1 wherein a plurality of flames are created and fed by a plurality of associated streams of oxygen and gaseous fuel.

3. A process as set forth in claim 1 wherein said oxygen is fed in an amount in excess of that required for the complete combustion of the fuel.

4. A process as set forth in claim 1 wherein said oxygen stream is fed as an annular sheath around said stream of gaseous fuel to isolate said flame from the melt by an annular sheath of oxygen and combustion products.

5. A process as set forth in claim 2 wherein said oxygen streams each form an annular sheath about an associated stream of gaseous fuel.

References Cited UNITED STATES PATENTS 2,874,038 2/ 1959 Ruhenbeck et al 59 3,115,405 12/1963 Boyd 7560X 3,141,763 7/1964 Foresi et a1. 7560 3,309,195 3/1967 Hutton 7560 3,316,082 4/1967 Barloga et al 756 0X 3,313,535 4/1967 Hopkins 26634.1

FOREIGN PATENTS 882,676 11/1961 Great Britain 7559 1,453,442 8/ 1965 France 7560 6411376 4/ 1965 Netherlands 7560 L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner 

